In physics, circular motion is a movement of an object along the circumference of a circle or rotation along a circular path. Consider a ball on a roulette wheel. It moves along a circular path of radius r. Other examples of circular motion are a satellite in an orbit or a ball on the end of a string. Circular motion is an example of two-dimensional motion in a plane. To begin the study of circular motion, consider a particle that moves at constant speed around a circle of radius r. This is called uniform circular motion.